Why were they called progressive amendments

Because they change and develop over time!

The Progressive Era 16-19 Amendments. This amendment protects the US citizens the right to vote on the basis of gender.

Explanation:

Significant changes enacted at the national levels included the imposition of an income tax with the Sixteenth Amendment, direct election of Senators with the Seventeenth Amendment, Prohibition with the Eighteenth Amendment, election reforms to stop corruption and fraud.